Population growth leads to territorial expansion and the integration of smaller groups into larger configurations comparable to city-states in some areas; many settlements become more urban. Class distinctions throughout the region result in increased demand for luxury items and there is an active exchange of goods along well-established trade routes between different environmental zones. Public and ceremonial architecture consists essentially of earthern mounds and platforms, some stone-faced. They serve as substructures for buildings of perishable materials and/or as the location of burials. Important burials are primarily in shaft-and-chamber tombs, often of considerable depth. Resist decoration on ceramic vessels and figures is common. Ecuadorian ceramics are mass-produced and are of lesser artistic quality than earlier works. Metalworking increases and reaches a high degree of artistry, particularly in Colombia, where many different styles exist. Metalworkers use both hammering and casting and a variety of surface decorating and enrichment techniques.